Maintenance
Following an overhaul , valves need to be tested . Image shows blind flanges being fitted to enable hydro testing and seat testing
“ Right now , valve stems , cages , plugs , membranes , actuators and positioners can be found in a wide variety of brands , type and sizes . So suppose valvemakers were to agree to restrict sizes of some parts to a limited number ? Yes , that would mean slightly more cost if instead of a 16 mm stem the manufacturer uses a 20 mm stem . But having fewer sizes would streamline manufacturing and also make it more attractive for manufacturers as well as stockists to keep inventories . And having ready access to parts would be a major benefit during a shutdown .”
Independent monitors
Mr Zegers is well-known throughout the valve industry , having set up a Dutch company that specializes in valve testing and inspection . However , he indicates that he is being increasingly approached by end users to act as an independent auditor and controller during shutdown activities . “ Despite the fact that we do not advertise this type of work , we are receiving more and more requests from chemical and petrochemical companies to be the eyes and ears of the asset owner in the overhaul shops .” Plants may of course decide to call in an expert like Mr Zegers , knowing that their own staff will be hard-pressed as it is during a shutdown . And that is quite understandable , given the wide scope of activities Mr Zegers is often tasked with . These vary from supervising safety , planning , sequence , progress , cost control , overview , parts supply , repair ( s ), QA / QC , testing , additional work , shipment , etc . In addition , this can necessitate monitoring the work of multiple revision shops . And the number and variety if valves involved can also be daunting to the inexperienced , taking in on / off valves , control valves and safety valves . “ In short , we ensure that a valve is overhauled correctly , in the shortest possible time and within budget so that the valve can be quickly reassembled so that it can be used until the next turnaround ,” concludes Mr Zegers .
Valve overhaul essentials To help newcomers better understand the intricacies of a valve overhaul , Mr Zegers kindly noted some of the key steps involved .
• Identification : all valves to be overhauled are provided with a metal label , with a list of steps to be taken such as cleaning , chemical cleaning , repairs , inspection , etc . Black squares are cut / punched out once each step has been taken , providing an immediate and clear indication of the valve ’ s progress .
• Dismantling : valves should be removed according to a certain order , depending on the application . Valves in utilities such as steam are often removed last and normally expected to be returned first .
• Pre-test safety valves : a pre-test indicates if the current set pressure of the safety valve is still within tolerance compared to the previously applied set pressure .
• Cleaning on-site : all valves must be carefully cleaned to remove residual products , which could otherwise be released during valve disassembly in the revision shop .
• Transport : valves should be transported in the correct position . Eg , safety valves should be transported vertically .
• Registration : upon arrival at the revision shop , the valves are registered and provided with the valve data sheet with all relevant data . Information and additional actions on documents are also attached to the valve . Eg , helium leak test , different positioner , extra tests , legal inspection , etc .
• Inspection : each valve is dismantled and subjected to an initial inspection .
• Cleaning : certain parts of the valve are cleaned and then sampled if necessary .
• Painting : parts that need to be preserved are provided with the correct coating after blasting . Consider heat-resistant paint for high temperature applications , appropriate colours for control valves ( normally open or closed ) and safety valves ( indicating whether or not fitted with a bellow ).
• Reassembly : when rebuilding the valve , use all new soft spares and any other spares needed to return it to a good working condition . Use OEM parts wherever possible . And use the right parts as regards for type of material , temperature range , pressure range , tightness class ( for stem sealing and gaskets ) when OEM parts are not available .
• Testing & final check : necessary to ensure the valve ’ s proper functioning and fitness for service . Safety valves are tested for set pressure and seat leakage according to international standards and national requirements . Most control valves are tested for ANSI FCI 70-2 with on / off valves tested according to international standards like : ISO 5208 or API 598 .
• Fugitive emissions : for safety and environmental reasons , more and more are valves to be tested for fugitive emission after overhaul . Fugitive emission tests evaluate the integrity of the external leakage of valve stem seals ( or shafts ) and body joints of isolating valves and control valves , intended for the application in volatile air pollutants and hazardous fluids . Standard ISO 15848-2 or end user procedures can be used to perform such testing . www . valve-world . net Valve World April 2023
31